Exactly four months ago Friday, Jets coach Rex Ryan stood behind a lectern at a preseason news conference and pondered, though not for long, a question about whether his defense would finish the season among the NFL’s top five in fewest yards allowed.

"We will be," Ryan said, citing "my history" as the reason for his certainty.

Ryan, long a successful defensive coach, was preparing to take on a larger role with the Jets’ defense, installing coverages before games and calling plays during them, just as he did in his first two seasons, 2009 and 2010.

Though the Jets’ young defense ended up showing some encouraging signs this season, it slipped in the past three games, and almost certainly will not meet Ryan’s lofty preseason expectations. With two games remaining, perhaps the final two of Ryan’s tenure, the 6-8 Jets are out of playoff contention and 12th in total defense, with 341.4 yards allowed per game. They are 28.6 yards per game from fifth place.

"I just assumed that’s where we’d always be," Ryan said of the top five.

He has rarely experienced otherwise. When he was Baltimore’s defensive coordinator from 2005-08, the Ravens finished fifth, first, sixth and second. In his first four years with the Jets, they ranked first, third, fifth and eighth. The Jets are currently 12.5 yards per game from eighth, though the gap might be too large to make up this late in the year.

"We’ve let him down from the standpoint of not being the defense during some parts of the games, that attacking defense that we know that we can be," said cornerback Antonio Cromartie.

The past three weeks haven’t helped. Against Miami, Oakland and Carolina, the Jets allowed their most, fifth-most and fourth-most yards of the season. In the first 11 games, the Jets allowed 325.5 yards per game. In the past three, they surrendered an average of 399.7. They gave up a rushing touchdown of 63 yards and passing touchdowns of 28, 31, 48 and 72 yards. They allowed 162, 140 and 155 yards after the catch in those three successive games, against opponents who rank 24th, 15th and 25th in total offense.

"The biggest thing that’s happened to us the last three weeks is we’ve missed tackles at inopportune times and they’ve cost us touchdowns," said defensive coordinator Dennis Thurman.

As the Jets try to at least reach the top 10 — they are 5 yards from the Giants, who occupy that spot — they face a significant challenge Sunday with Cleveland wide receiver Josh Gordon. He leads the NFL in receiving yards per game (122.3), yards per catch (19.8), catches of 20-plus yards (25) and catches of 40-plus yards (nine). He is second in yards after the catch, with 614, according to Pro Football Focus.

This might not bode well for Cromartie, who has allowed 20.2 yards per pass completed against him (most in the league) and 367 yards after the catch (third-most in the league), according to Pro Football Focus.

Pass defense has been an issue for the Jets all season, be it with failing to contend for deep balls earlier in the year or missing tackles on catch-and-run plays recently. The Jets have allowed 12.4 yards per completion, 25th in the NFL. They must decide in the offseason if they want to retain Cromartie, who is entering the final year of his contract and is due to count $14.98 million against the salary cap next season.

But the Jets’ front has impressed. They lead the NFL with 3.2 yards per carry allowed. Tackle Sheldon Richardson is a potential Defensive Rookie of the Year. End Muhammad Wilkerson, a third-year pro, is the Jets’ overall best player and leads them with 10 sacks. The front’s second-year players have all improved: nose tackle Damon Harrison, rush outside linebacker Quinton Coples and weak-side linebacker Demario Davis.

“I feel like we’re playing at an elite level compared to other defenses’ (fronts) in the league,” said third-year nose tackle Kenrick Ellis, who rotates with Harrison. “We’re so young (that) the ceiling is so far from where we’re at right now.”

Whoever coaches the Jets in 2014 will have a strong foundation with this defensive line.

“I think if you would ask any coach, really, if you were going to build a defense, you would want to build it from inside out,” Ryan said. “There’s no reason why they shouldn’t be one of the top groups in the league.”

But will Ryan be around to see it blossom?

“I think a big part of why the Jets’ defense has always been special is Rex,” Davis said.

Ellis raved about the impact of Ryan’s increased involvement this year. He forced linemen to be more aware of pass coverages and the secondary’s role than they were last year under coordinator Mike Pettine, and “now we have a fuller picture of the defense” that lets all players grasp the domino effect of each other’s duties, Ellis said.

Many of these Jets defenders will return next season and aim for the top five. If Ryan is absent, “that would be tough, man,” said safety Dawan Landry. “It’s hard to imagine a Rex Ryan team without Rex, so I can’t picture that at all.”